1. Field of the Invention
The present invention generally relates to a fiber-optic cable. More particularly, the present invention relates to an air-blown fiber-optic cable, which is installed using air pressure within a pipeline having a small diameter.
2. Description of the Related Art
Currently, air-blown fiber technology exists in which the construction of communication networks laid underground includes tubes mounted within a variety of pipelines (for example, sewer pipelines), which already have been laid under the respective ground areas, and an optic cable is installed into the tubes by means of equipment using air pressure without the engineering work typically associated.
Such an air-blowing installation-type construction method, which applies the air-blown fiber technology, is used for constructing various kinds of communication networks—particularly, optical communication networks. The results are reduced costs and simpler construction as compared to the existing construction method for installing communication cables under the ground (for example, pulling-type construction method). The reason for these advantages is that the air-blowing installation-type construction does not require new piping or engineering works such as excavation and restoring landscaping for laying the new piping under the ground.
FIG. 1 is a cross-sectional view showing the structure of a loose-tube optic cable according to the conventional art. Such an optic cable is associated with the pulling-type construction method, in which the optical cable is pulled and pushed during the installation of it into piping. However, when such work is performed, an excessive tension is directly applied to the optic cable, thereby increasing the risk of deteriorating the characteristics of an optic fiber 130. To prevent this deterioration, the optic cable should have a structure for maintaining some tension resistance required for the construction method. As shown, the optic cable consists of a central tensile member 110, a plurality of loose tubes 150, a waterproof tape 160, an outer-layered tensile member 170, and an outer sheath 180.
The central tensile member 110 provides the optic cable with tension resistance and is placed in the center of the cable. The central tensile member 110 is made of, for example, FRP (fiberglass-reinforced plastic), and a layer 120 coated on the central tensile member 110 is comprised of a highly polymerized compound, such as PVC (polyvinyl chloride) and PE (polyethylene).
A plurality of optical fibers 130 is mounted in the respective loose tubes 150, and a hollow space of the loose tubes 150 is filled with the jelly compound 140 for the purpose of protecting the optical cables 130 from the external shock and absorbing moisture permeating the loose tubes 150. In addition, the loose tubes 150 can be gathered helically around the central tensile member 110.
The waterproof tape 160 surrounds the loose tubes 150, thereby preventing moisture from entering the interior of the tubes.
The outer-layered tensile member 170 encircles the waterproof tape 160, improves the tension resistance of the optic cable and can be made of strength yarn, such as glass yarn.
The outer sheath 180 is placed on the outermost part of the fiber-optic cable and made of a highly polymerized compound, such as PVC (polyvinyl chloride), PE (polyethylene), hytrel, nylon, and polypropylene, and formed by the extrusion process. Additionally, the sheath 180 may comprise rip cords adjacent to the inner wall thereof for facilitating its peeling off action.
As explained above, the loose-tube optic cable according to the conventional art is adapted for the pulling-type construction method and must have the elements, such as the coated central tensile member and the outer-layered tensile member, for maintaining the levels of tension resistance required for such a method. Accordingly, this requirement increases the weight and the outer diameter of the optic cable. Thus, it is not possible to employ the optic cable of this type in the air pressure-type construction method in which fiber-optic cables should be of a small diameter and weight.